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Harbor Freight MIG Welder Modifications

I have an old (maybe 20 years Old) Harbor Freight Mono-Mig 160 220V welder. It's set up for Argon/25% CO2 Gas. Over the years it's served me fairly well. Finally I got fed up with the inconsistent wire speed and decided to rebuild the entire welder. What I did:

1) Replaced the wire feed motor with a automotive worm gear electric window motor. I paid ~$25 for this. I got a few, and found one that I could control the speed down to practically zero with ample torque. The nylon gear train, crappy hobby motor, and worthless speed controller were trashed. I bought a DC motor PWM controller for about the same price that would work off of 24V DC. Next I trashed the 24V AC transformer, and used a Laptop PC notebook power supply that will work off of 220V input. Used the stock rollers and tension adjustment, but trashed the rest of the drive assembly. After this I have a super accurate speed control with a ton of torque that I'll match against any in the business.

2) The Mono Mig 160 has a decent sized transformer and also has a nice sized inductor. I installed a 76000 uFD 70V electrolytic capacitor between the + side of the rectifier, and the transformer to inductor connection. This really HELPS a LOT with stabilizing the Arc. I got this idea from a Hobart MIG schematic I found on the Web. A 50V capacitor should be enough.

3) I replaced the Bridge Diode assembly with one I made myself. Not necessary but I was having Fun.

4) I trashed the wimpy 220V fan, and installed a real 220V fan. Helps a lot with the duty cycle.

5) Trashed the Relay, and replaced with a 40 Amp Solid State Relay.

6) Added a 35 Amp Circuit breaker to the back.

A completely new machine that's a pleasure to use anytime. No more fussing with wire speed, the Arc is much more stable.

Re: Harbor Freight MIG Welder Modifications

Sounds like quite a rebuild, and something I would like to do with a new unit.

I'm not entirely sure about a PWM controller, but I know (first hand) that a switching power supply can cause some problems with a stepper motor driver. You probably already know the switcher is using an IC to cut the power on and off to keep a DC level, not entirely unlike your PWM controller is doing to the motor. I think the swtiching noise on the supply can mess with the switching circuit for the motor and cause some funny pulses. Since your setup is already working, this isn't likely a big deal. But if you see any motor drive problems you might swap a battery for the switching power brick to see if that is what is going on.

Re: Harbor Freight MIG Welder Modifications

The window crank motor assembly is a Brush motor, not a stepper. I tried the PWM controller with the stock hobby motor and it worked okay for a while.. then it started smoking. Therefore the electric window motor. No issues at all. Plus with the regulated Notebook power supply, the motor speed is constant at all times. Also with the way I rewired it, the torch is only hot when the wire is moving. I'm not sure if the later model HF MIGs have an inductor on the output. I've seen some cheap MIGS which do not. Gotta have the inductor to call it a real MIG. The capacitor was a huge improvement too.

Re: Harbor Freight MIG Welder Modifications

If I'm not mistaken weren't the early Harbor Freight wire feeders mostly made in Italy?

In any case it sounds like you have a really intriguing project. My 151 is good as long as the wire control is somewhere near the middle. I had given some thought to putting a higher quality potentiometer in it and seeing if that alone would do any good.

If you don't mind my asking, what kind of use did your welder see over the course of its evidently long service life with you?

Re: Harbor Freight MIG Welder Modifications

Not sure if this one was made in Italy or not. I did see "Made in Italy" on the voltage select switch, so that may be true. I did a fair amount of Auto Body work. I wanted to butt weld in sheet metal, grind it off, and a thin coat of bondo to make it perfect. It was difficult to get the wire speed slow/consistent enough on the lowest setting to do this effectively. On the higher settings with higher wire speed it always did a decent job on thicker metal. Issue was thin body panels without burning thru. The stock wire drive motor/nylon gear/controller/tensioner just wasn't consistent and changed speed as I was welding (and was NOISEY as heck). The drive motor/gear train just couldn't handle the torque required. I burned out the original controller a couple times, but could fix it (Pot and Transistor usually). Now with the new motor/PWM controller, I can set the wire speed as slow as I need and the pinch wheel tension high enough so the wire never slips. Don't forget to add that capacitor either. With the modifications I made it's a whole new machine.. Nothing's perfect, but this is decent on thin metal now with .023 wire. I might try even smaller wire if I can find it. I'll take some pictures and post them.

Re: Harbor Freight MIG Welder Modifications

Very cool man. I use my 151 mostly for small fence repairs and the like (welding together custom hose brackets and pipe fixtures from time to time, etc etc.)

So mine always has .030 flux wire in it. I can still effectively weld sheet metal down to 22 gauge with that setup but it is difficult to be consistent as you say because of the inconsistent wire feed.

You've definitely given me some food for thought for a future potential project to undertake myself.

Re: Harbor Freight MIG Welder Modifications

CDG.. Never had any problem on higher current settings with moderate wire speed. I'm sure your 151 will do fine for your application. The motor controller board on my machine did burn out a couple times, but wasn't hard to replace the Potentiometer and the drive Transistor. The much newer 151 probably has a better motor controller design than mine.

Re: Harbor Freight MIG Welder Modifications

I certainly don't have as many problems with the controller board and pot as you have had. When I got my 151 welders (2 for 20 bucks not working), I had to replace the controller board in the one but since then the one welder I kept has served me quite well.

I was mostly thinking about the possibilities of a power window motor. I can weld effectively as the unit is right now as I said, but the wire feeder really takes a light hand to adjust properly which can get a little frustrating. Having a higher torque motor would be nice at least.

All in all I'm still amazed at the value my Dual Mig welder really is. I effectively paid 10 bucks for it after I was done putting parts in the two units I picked up and selling one of the units at a profit. It has its flaws, but I enjoy having a beater welder in the shop.

Re: Harbor Freight MIG Welder Modifications

I just bought a Model 151 HF welder and will probably live with the standard wire feed for now, but I am curious, would you recommend the capacitor to stabilize the arc even if I don't change the wire feed motor? I'm especially interested if this will make it easier for a first time welder. Is this useful in both flux core and gas mode?

Re: Harbor Freight MIG Welder Modifications

Holabr.. I've never used Flux Core wire or a Dual 151.. only Gas here. All I can say is that on the lowest setting on my Mono MIG 160 (20 years old), with the additional capacitor, welding is much more stable than without the cap. It's much easier to keep a constant arc. I'd add a big cap if your Dual 151 doesn't have one. You need to keep the inductor connected directly to the ground lead, and put the cap between the + output of the full wave rectifier, and the junction of the transformer and the inductor. I added two large 36000 uF, 70V electrolytic caps in parallel. The Hobart schematic lists a 50V electrolytic capacitor. Your Mileage may Vary. Good luck, I'm very happy with my HF MIG now.. was so-so before.

Re: Harbor Freight MIG Welder Modifications

My hats off to anyone that can play with electronics and figure out how to improve these units. If I can't see-smell-or taste it--I ain't messing with it. Although I usually don't understand what y'all are doing,I do enjoy reading about what you did.

You guys are missing the boat...these things are everywhere "broken" for cheap---buy them for a song and remanufacture them for profit.Everyone will be happy.

Re: Harbor Freight MIG Welder Modifications

Yeah.. I get a kick out of buying used/beat up items (Cars, Tools, Houses, Furniture etc.) and rebuilding them better than new. By the time I'm done, I'm sure I could have bought a brand new item for less money, but still keeps the Alheimer's away..

Re: Harbor Freight MIG Welder Modifications

That motor looks identical to the one I used, but $5 cheaper! I don't have any pics, but can take some this weekend. As far as how I adapted it to the tension system:

1) Removed the entire stock drive assembly from the welder.
2) Removed the "Hobby" motor.
3) Split the gear case (screws and pins I believe), removed the gears. Keep the entire
top piece of the stock drive assembly. Shave off any plastic that will extend below the
welder top sheetmetal.
4) Drill a larger hole (if necessary) in the top piece of the stock drive assembly to accomodate the window motor drive shaft.
5) Remount the top piece of the stock drive assembly to the top sheet metal piece of the welder.
6) Mount the window drive motor to a thin piece of sheet metal that's larger
than the entire stock drive assembly. On my welder, I had to cut out a small piece of the welder top sheet metal to make a flat surface to mount the window drive assembly.
7) match the hole in the stock drive assembly with the window drive motor, and screw it to the top sheet metal of the welder.
8) I had to grind the window drive motor shaft square to accomodate the stock drive wheel.
And I used like 5 washers to hold it at the right height. for the wire feed. Other options are available.

Re: Harbor Freight MIG Welder Modifications

I'm not an electronics kind of guy but was wondering about the capacitor mod. Is any voltage greater than the "open circuit voltage" of the welder OK to use? What would the minimum mf value to be effective be? Is this a case of bigger is always better?
Thanks for the help.

Resistor change on MX033

(Your tread)
I did increase the PWM frequency of the PWM controller to around 8 Khz from 100 Hz by changing a resistor value. This further helped with the very slow torque.

I use the MX033 in a different application (speed control on DC motor)
And my motor torque is to low in the mid speed range
Can you tell me what resistor on the PCB have to be changed to
increase the PWM frequency (factory set @ 100Hz) , and to what value did you change it?

Re: Resistor change on MX033

R4 have to be changed in value the change the Frequency
The smaller this is the higher the frequency gets

R*C on the opamp

Try a few resistor values to see if it helps with the torque on the mid range speed
On my DC motor.

I know this is a old tread but i'm also using the MX033 controller

(Your tread)
I did increase the PWM frequency of the PWM controller to around 8 Khz from 100 Hz by changing a resistor value. This further helped with the very slow torque.

I use the MX033 in a different application (speed control on DC motor)
And my motor torque is to low in the mid speed range
Can you tell me what resistor on the PCB have to be changed to
increase the PWM frequency (factory set @ 100Hz) , and to what value did you change it?

Re: Harbor Freight MIG Welder Modifications

Hello, if you are even still on this forum I could use your help. I have inherited the same monomig 160 from my dad. I need a new contactor and something tells me its going to be hard to find. Did you replace that part also and what and where did you find the contactor.